The present invention relates generally to a document reproduction machine and, more particularly, to an apparatus and method for reducing the effects of airborne contaminants which adhere to the surface of optical components within such a machine, such as mirrors, transparent ROS windows, lenses and the like.
A constant problem in operating a xerographic copier/printer is the need to reduce the effects of airborne contaminants which are unavoidably created during machine operation. These contaminants include toner particles originating in the development station used to develop the latent image formed on a photoreceptor; dust from copy paper transport, particles loosened from the document handler, degraded portions of a doctor blade or transfer roll and the usual dirt and dust from the ambient. One source of image quality degradation is the adhering of the contaminants to the surface of the optical components which are arranged along an optical path to either scan a document and form an image on a CCD array, as in a RIS scanner, or to expose a photoreceptor drum with a modulated radiation pattern generated by a Raster Output Scanner (ROS) system. Examples of the components which may become contaminated are: the bottom surface of the document platen, the mirrors and lenses in a document scanning system and the mirrors and lenses in a ROS system. These components all can accumulate, over time, sufficient contaminants adhering to a surface to reduce exposure at the photoreceptor by partially blocking light reflected from or transmitted through the component. Particles can also reduce contrast in an image exposure profile at a photoreceptor by scattering light reflected from a mirror component.
Various methods of reducing these contamination problems are known in the art. One technique is to establish a positive air flow across the exposed surface to prevent the adhesion of the contaminants. Another expedient is to isolate the components in a housing so as to remove them from the airborne contamination. This is accomplished, for example, by placing the ROS optical scanning components within a ROS housing. The modulated ROS scanning beam then exits the housing by means of a transparent exit window. The transparent exit window, however, is still susceptible to contamination on the outside surface. The air flow solution has been found to be partially effective in removing larger diameter contamination particles (above 10 microns). For smaller particles, the van der Waals force becomes comparable to the electrostatic forces dominating the adhesion of the larger diameter particles to the surface.
It is, therefore, an object of the present invention to reduce the rate at which airborne contaminants are deposited on the surface of optical elements such as mirrors, windows and lenses used in a xerographic reproduction machine.
It is a further object to reduce the contaminant adhesion in a relatively inexpensive manner.
It is a still further object to reduce the adhesion of smaller diameter particles while preventing the adhesion of larger diameter particles by a positive air flow. These and other objects are achieved, in one embodiment, by coating the affected surface with a transparent coating of a material having a low surface energy. In another embodiment, the lateral conductivity of the coating is controlled to increase dissipation of electrostatic surface charge. In a still further embodiment, an air-assist cleaning step is added to improve efficiency. More particularly, the invention relates to a document reproduction machine wherein a plurality of optical components are located within a machine frame and wherein at least one of said optical components has at least one surface subject to adhesion thereon by airborne contamination particles, a method for reducing the adhesion of said particles on said surface comprising the steps of: selecting a material having a low surface energy, and forming a transparent coating of said material on the surface of at least one of said optical components.